The offshore drilling industry is constantly striving and searching for increased oil production. In pursuing that interest, offshore apparatus have been erected and wells drilled in ever deeper waters. In addition, the offshore oil drilling industry is using larger diameter pipelines to obtain large production rates and to reduce the cost per gallon of oil.
A problem common to all offshore apparatus is providing the connection from an above water facility to a pipeline which lies on the bottom of a body of water. One typical method of providing the connection is the use of a "J-tube" riser guide member which is a continuous tubular structure having the shape of a "J" and through which a riser pipeline is pulled from the bottom of a body of water to the above water facility. The thus pulled pipeline portion, i.e., the riser, provides the fluid flow path from the above water facility to the pipeline at the bottom of a body of water. (See, for example, the discussion in Matthews, Jr., U.S. Pat. No. 3,595,312, issued July 27, 1971.)
The "J-tube" riser is useful for riser pipeline diameters up to about 12 inches. For riser pipelines having a diameter greater than 12 inches, the high pulling force required to install the riser is a major deterrent to further use of the "J-tube" riser. On the other hand, the "J-tube" riser does have the advantage of a controlled and simple installation process which does not require elaborate pipeline manipulating equipment.
For pipeline diameters greater than 12 inches, a "bending shoe" riser guide member, as shown for example in Broussard et al., U.S. Pat. No. 3,466,882, issued Sept. 16, 1969, can be used. This riser installation device has been used for large diameter riser pipelines because it does not require the large pulling force of the J-tube riser, and therefore can more easily and readily be used with larger pipe diameters. On the other hand, the bending shoe riser has a major disadvantage because it requires an elaborate and precise installation procedure which necessitates the use of complex instrumentation and hardware. This is especially important at deeper water depths.
It is therefore an object of the present invention, to provide a new riser guide member which has the advantages of both the conventional "J-tube" riser and the "bending shoe" riser without having the disadvantages of either. In this sense, a synergistic result is obtained. Other objects of the invention are to provide a riser guide member which is simple and easy to use, which does not require unusually large pulling forces, which does not require elaborate and precise installation procedures, which does not require complex instrumentation and hardware, and which provides for a stable and controlled riser installation.